The present invention relates to a method and an apparatus for measuring the thickness of a film on a substrate, and a substrate processing apparatus utilizing the same. The method and apparatuses of the present invention can be advantageously employed especially in effecting real-time detection and monitoring of a film thickness of a substrate on a side being processed during processing. It should be noted that xe2x80x9cmeasurement of a film thickness of a substratexe2x80x9d in the present invention means not only measurement of a film thickness of a substrate, but also detection or observation of a condition of the substrate, such as the presence or absence of a metallic thin film formed on the substrate.
As a conventional technique of the above-mentioned type, Unexamined Japanese Patent Application Public Disclosure (Kokai) No. 7-251371 discloses the technique of emitting light from a distal end of a glass fiber to a measurement surface of a substrate during polishing, and receiving the light reflected by the measurement surface through the glass fiber. The glass fiber guides the reflected light to a film thickness measurement control unit.
In the above-mentioned technique of emitting and receiving light through a glass fiber, a measurement error is likely to occur due to the presence of drops of liquid formed on the substrate during polishing. Further, it is required to strictly control the distance between the distal end of the glass fiber and the measurement surface of the substrate.
Unexamined Japanese Patent Application Public Disclosure (Kokai) No. 10-264017 discloses the technique of placing a polished substrate in a cleaning liquid in a cleaning tank, inserting a distal end of an optical fiber into the cleaning liquid and bringing it to a position in the vicinity of a measurement surface of a substrate. Those steps are followed by emitting light to the measurement surface, and introducing, the light reflected by the measurement surface through the optical fiber to a film thickness detection apparatus.
In the above-mentioned method of placing the distal end of the optical fiber in the cleaning liquid, it is necessary to control the distance between the distal end of the optical fiber and the measurement surface of the substrate. Further, a large apparatus is required.
In view of the above, the present invention has been made. It is an object of the present invention to provide a method and an apparatus for measuring the thickness of a film formed on a substrate, and a substrate processing apparatus utilizing the same, which have simple arrangements and are capable of effecting real-time and highly accurate measurement of a film thickness of a substrate during processing, such as polishing.
In accordance with an aspect of the present invention, there is provided a method for measuring a thickness of a film on a substrate comprising directing a jet of a light-transmitting liquid towards the film to form a column of the light-transmitting liquid reaching the film, directing a light through the column of the light-transmitting liquid towards said film, receiving the light reflected from the film through the column of the light-transmitting liquid, and measuring the thickness of said film upon receipt of the light reflected from the film. The diameter of the column may be uniform.
In accordance with another aspect of the present invention, there is provided an apparatus for measuring a thickness of a film on a substrate comprising a first conduit having a distal end (i.e., an end closest to the film), which is directed to and spaced away from the film. The first conduit discharges a jet of a light-transmitting, liquid from the distal end thereof towards the film to form a column of the light-transmitting liquid extending between the distal end of the first conduit and the film, the diameter of the column being uniform. A light emitter is provided for emitting light toward the film through the column of the light-transmitting liquid, and a light receiver is provided for receiving the light reflected from the film through the column of the light-transmitting liquid to enable measurement of the thickness of the film on the basis of the light reflected from the film.
The light emitter may comprise a light-emitting optical fiber having a distal end (i.e., an end closest to the film) directed to the film to direct the light towards the film through the column of the light-transmitting liquid. Further, the light receiver may comprise a light-receiving optical fiber having a distal end (i.e., an end closest to the film) directed to the film to receive the light reflected from the film. The optical fibers of the light emitter and the light receiver may also be integrally formed so that only a single light emitting/light transmitting optical fiber is provided.
Alternatively, the first conduit may be provided with a light transmitting member such a lens liquid-tightly separating the inside and outside of the first conduit, and an optical system provided outside the first conduit and optically connected to the first conduit so as to direct light from the optical system through the light transmitting member provided on the first conduit so that the optical system can direct the light towards the film through the first conduit and the column of the light transmitting liquid. The first conduit may further be provided with an optical system provided outside the first conduit and optically connected to the conduit so as to receive the light reflected from the film through the column of the light-transmitting liquid, the first conduit and the light transmitting member.
The film thickness measurement apparatus may further comprise a second conduit inside of which the first conduit is positioned so that the second conduit receives the light-transmitting liquid which has impinged on the film and radially spread. The second conduit may be connected to a pump to draw the light transmitting liquid spread radially.
In accordance with a further aspect of the present invention, there is provided an apparatus for treating a substrate bearing a film on the surface of the substrate comprising a holder for holding a semiconductor wafer, and a film thickness measurement device constructed as stated above. The substrate treating apparatus may be a polishing apparatus for polishing a substrate. The polishing apparatus comprises a turntable having a polishing surface and a substrate holder for keeping a substrate in contact with the polishing surface to polish the substrate, in which the first and second conduits are provided through the turntable. The second conduit opens at the polishing surface so as to be sealed from the outside thereof by the polishing surface engaged with the substrate, and the first conduit has the distal end spaced from the substrate engaging with the polishing surface. There may also be provided a plurality of sets of the first and second conduits.
When the diameter of the column of the light-transmitting liquid is made uniform, the size of a measurement spot formed on the film or measurement surface is determined, regardless of the distance between the distal end of the first conduit, through which the light-transmitting liquid is emitted towards the film, and the film.
In accordance with a further aspect of the present invention, there is provided an apparatus for polishing a substrate comprising a turntable having a polishing surface and an axis for rotation. A substrate holder holds a substrate having a film on its surface so that the film is engaged with the polishing surface. A film thickness measurement device comprises a light emitter for emitting light toward the film, a light receiver for receiving the light reflected from the film to enable measurement of the thickness of the film on the basis of the light reflected from the film, and an optical system having an optical path extending through the turntable from the center of the turntable to a predetermined radial position in the turntable. The optical path includes a proximal end opening in the polishing surface and extending axially, and a distal end opening in the polishing surface at the predetermined radial position so that the light from the light emitter is introduced into the optical path through the proximal end, lead to the distal end and directed to the film and the light reflected from the film is returned to the proximal end to exit the optical path to enable the optical receiver to receive the reflected light.
The foregoing and other objects, features and advantages of the present invention will be apparent from the following detailed description and appended claims taken in connection with the accompanying drawings.
In the following detailed description, certain specific terminology will be employed for the sake of clarity, and a particular embodiment is described. However, it is to be understood that the name is not intended to be limiting and should not be so constructed inasmuch as the invention is capable of taking many forms and variations within the scope of the appended claims.